Such a multibranch harness conventionally comprises a network of conductors (the network being continuous or optionally being made up of separate segments spliced together). The conductors are twisted together. The branches are connected in accordance with the pre-established layout, thereby constituting individual interactive links between the connection points.
There are a wide range of possible uses for such harnesses. In particular, they are used in land, air, or sea mobiles, for powering items of equipment on board the mobiles and for transmitting data signals between all or some of the items of equipment or appliances. In a good many applications, such harnesses need to have high-performance protection against electromagnetic interference, in addition to being strong enough to withstand considerable shocks, vibrations, and heat and/or chemical attack, in particular.
Independently from the problem of providing high-performance electromagnetic protection, the use of braiding is known for covering a network of conductors, mainly to provide cohesion therefor or to improve the overall strength thereof. Such braiding leaves the network relatively easy to handle so as to facilitate laying it and inserting it to the various points at which its branches are connected in the mobile in which it is used.
The overall-strength braiding is often a textile fabric, or is sometimes made of metal. In general, it provides the network with good mechanical properties, but cannot per se directly provide high electromagnetic protection, in particular at the forks.
To obtain high electromagnetic protection for the harness, two techniques are currently used for solving the problems of providing protection at the forks.
A first one of those techniques consists in using initially independent branches that are shielded individually by means of metal braiding, and in connecting them together in the desired layout by means of shielded splice boxes. The network is thus made up at the same time as the forks are shielded, by means of the splice boxes.
The shielded network obtained by using the first technique has excellent electromagnetic performance levels, due both to the uniformity of the initial shielded branches, which are equivalent to so many individual shielded cables, and to the low transfer impedance between each branch and the corresponding splice box. The network also has generally satisfactory mechanical properties. However, it is heavy, expensive, bulky, complex, and inflexible, due to it being made up from shielded cables constituting the branches that may have very different numbers of conductors and very different cross-sectional areas, and from splice boxes which are very often also different from one another.
The second technique consists in using a network of conductors, with the conductors co-operating with one another to define the different branches at the different forks in accordance with the layout of the harness, in shielding the branches by means of metal shielding braids made previously and threaded over each of the branches, and in threading heat-shrinkable metal-plated sleeves over the various forks to provide continuity in the shielding with the above-mentioned braids.
The shielded harness made by using the second technique offers advantages but also suffers from drawbacks compared with the harness made by using the first technique. The second harness is lighter in weight, less expensive, more compact, simpler, and more flexible. However, with the second technique, the electromagnetic performance levels of the harness are poor and often insufficient, as are its mechanical properties, in particular its ability to withstand vibration which, as a result, reduces the electromagnetic protection provided.
The low performance levels are partly a result of the braids being threaded on, which deforms their shape and gives rise to relative displacement of the braiding wires, with gaps or holes being created between the wires. Such defects prevent intimate contact between the wires in each braid, and are accentuated when in the presence of vibration which causes the wires to be displaced relative to one another and on the conductors in the network. Such displacement gives rise to abrasion, whereby the insulation on the conductors is degraded.
The low performance levels are also a result of the electrical contacts between the sleeves and the braids being inadequate and/or being degraded under the conditions in which the harness is used. This is due to the contact surfaces being small and to the material of which the sleeves are made being different from the material of which the braids are made, thereby giving rise to prohibitive transfer impedance levels at the forks.
Furthermore, independently from the electromagnetic shielding of the network of conductors, and from the continuity in shielding over the forks, those two techniques require end connectors to be connected subsequently to the harness, at the ends of the various branches, and electromagnetic protection to be provided at the rear connection ends of the connectors. Mounting and electromagnetically protecting the connectors involves handling the shielding braids of the branches roughly so as to thread them over the rear ends of the connectors and to lock them thereon. Such rough handling irretrievably degrades the shape of the braid, and does not enable satisfactory continuity in shielding to be obtained between the connectors and the network of conductors, at least for some uses of the harnesses.
An object of the present invention is to avoid the drawbacks of shielded multibranch harnesses that are made by using those known techniques.